To simplify the following discussion, the present invention will be explained in terms of a typical inkjet printing mechanism; however, it will become apparent from the following discussion that the present invention may be applied to a much wider class of printers. Inkjet printing mechanisms are relatively inexpensive, and hence, inkjet printers are well suited to the personal computer market where capital cost is a key factor in the selection of a printer. In addition, this type of mechanism is employed in very large format printers such as those used to generate architectural drawings and in high-resolution color printers used to create color prints from digital photographs.
Inkjet printers utilize a printing mechanism in which a print head prints a swath of dots as the print head moves across the page in the horizontal direction. The swath typically includes one or more vertical columns of dots. After each swath is printed, the paper is typically advanced in the vertical direction by an amount equal to the height of the swath. The vertical positions of the dots within a swath are determined by the positions of the inkjets in the print head, which are fixed at manufacturing and controlled to a very high accuracy. The horizontal position of each column of drops is controlled by firing the droplet mechanism at times determined by a clock as the print head moves across the paper at a constant speed in one prior art mechanism. The accuracy of the dot placement depends on the horizontal actuator propelling the print head at a very constant speed. Any variation in the print head speed leads to errors in the dot positions.
The separations between successive swaths must be tightly controlled to avoid printing artifacts. Print registration artifacts are easily discerned in multi-color printing, since such artifacts can alter the tone of the perceived color. Tolerances of less than a micron are required in high-resolution color printing.
In principle, the accuracy of the horizontal dot placement can be improved by utilizing a precision actuator or some form of absolute positioning mechanism. However, such systems are costly, and, as noted above, the initial cost of the printer is a key factor in the selection of a printer.